Technical Field
The present subject matter relates generally to the control of hydraulic automatic transmissions for motor vehicles and, more particularly, to control over transmission operational modes based on the velocity or proximity of obstructions to the motor vehicles.
Description of the Technical Field
Some hydraulic automatic transmissions provide for reducing the parasitic load imposed on vehicle engines during periods when the vehicles are stopped. Examples of such a transmissions include examples supplied by Allison Transmission of Indianapolis, Ind. such as the 3000 HS, 4000 HS and 4500 HS automatic transmissions. These transmissions operate at reduced pressure upon braking the vehicle to a complete stop even while the transmission remains “in gear.” This operational mode reduces the load on the engine and the amount of fuel used to maintain a minimum idle speed. Allison calls this mode of transmission operation “reduced engine load at stop” (RELS).
In the Allison transmissions return to the normal operating mode from RELS mode occurs upon indication of brake release. On vehicles equipped with pneumatic brakes such indication is a change in brake system air pressure. This results in a lag between brake release and the transmission's return to normal operating pressure. Operators may notice hesitation or initially sluggish acceleration on the part of a vehicle after a stop.